rt2x00: Sync rt2800 MCU boot signal with Ralink driver.

Latest versions of the Ralink rt2800 family drivers use 0 as the token value,
not 0xff.

Signed-off-by: Gertjan van Wingerde <gwingerde@gmail.com>
Signed-off-by: Ivo van Doorn <IvDoorn@gmail.com>